How do I get music onto my iPad Mini (iOS 7) which hasn't been purchased on the iTunes Store?

Connect your iPad to your MacBook Pro with a USB cable. Open up iTunes, and click on your the iPad button (located on the top bar along with albums, artists, radio, etc.). Once your into your iPad settings, on the same top bar click music, and it will show a sync music checkbox. Click that box, then select either entire music library, or selected playlists, artists, albums, and genres. If you choose the selected music option choose the music you want. Once you've done that, click sync on the bottom right, and wait for the music to sync to your iPad. Disconnect after ejecting. Hope this helps.

If it says that you need to remove media from the device before syncing, its a bit more complicated. If you have all the already on your iPad on your MacBook Pro, or if you purchased it through with your Apple ID, then go ahead and sync, because all that music can be resynced or downloaded to you iPad. If your existing music is from another computer, you could use home sharing to move the music over to your MacBook Pro.

To use home sharing, go under the File menu in the menubar, and find home sharing. Turn home sharing on on your MacBook Pro and the computer that your music was from originally. Sign in with the same Apple ID on both. You can now move music from the original computer to your MacBook Pro. Once you've done that, sync the music to your iPad as I explained in the first paragraph.

iTunes: Syncing media content to iOS devices and iPod - http://support.apple.com/kb/HT1351 - detailed example: https://discussions.apple.com/thread/4090536?answerId=18860187022#18860187022

iTunes 11 for Mac: Set up syncing for iPod, iPhone, or iPad - http://support.apple.com/kb/PH12113 - including manual syncing